The present invention relates generally to an electrical jack for use in conjunction with a pin-plug, and more particularly to a resilient contact member which engages resiliently with a pin portion of the pin-plug inserted into the jack.
There have been proposed various kinds of the jack. FIG. 1 is a cross section showing an embodiment of the known jack. A jack 1 comprises a resilient contact member 2 which is secured to an inner wall of a housing 3. The contact member 2 is formed by bending a metal strip of a relatively large width into a substantially U-shaped form. The contact member 2 comprises a fixed leg portion 8 and a movable leg portion 10 connected to the leg portion 8 by means of a U-shaped bent portion 6. When a pin-plug 4 is inserted into the jack 1, the movable leg portion 10 is displaced from a position illustrated in FIG. 1 by a chain line due to an engagement of the movable leg portion 10 with a pin portion 5 of the plug 4. Each time the pin-plug 4 is inserted into and pulled out of the jack 1 the bent portion of the contact member 2 is deformed and thus is fatigued. Therefore a resiliency or elasticity of the contact member 2 becomes gradually decreased. In an extreme case the bent portion 6 might be deformed beyond its elastic limit and could not return to its original position. In this manner a contact pressure of the contact member 2 with respect to the pin portion 5 becomes small and thus an electrical property of the pin-plug and jack connection is deteriorated to a great extent.
In order to avoid the above mentioned drawback of the known jack there have been devised several jacks. FIG. 2A shows an embodiment of such a jack. In this jack 1 a projection 7 is formed on the inner wall of a housing 3 and a fixed leg portion 8 of contact member 2 is provided with a hole 9 as illustrated in FIG. 2B. As shown in FIG. 2A the contact member 2 is secured to the housing 3, while the projection 7 is inserted into the hole 9. The projection 7 has such a length that it can limit the displacement of the movable leg portion 10 of the contact member 2.
FIG. 3 shows another embodiment of the known contact member. In this embodiment a part of a fixed leg potion 8 of a contact member 2 is cut and a projection 11 is formed by raising the cut lug. In the embodiment the projection 11 serves to limit excessive displacement of the contact member 2.
The contact members illustrated in FIGS. 2 and 3 can overcome the disadvantage of the contact member shown in FIG. 1 and the movable leg portion 10 can be effectively prevented from being deformed beyond its elastic limit. However it is rather difficult to manufacture such contact members. It is apparent that the manufacture of such contact members requires at least one additional step. Particularly in case of a jack of small size the contact member could not be formed from a relatively wide metal strip, but has to be made of a thin metal strip such as a metal wire. In this case the above mentioned reinforcing means could not be applied at all.
The inventor has proposed in a copending U.S. patent application Ser. No. 71,163 filed on Aug. 30, 1979 an improved contact member for use in a jack. FIG. 4 shows an embodiment of such an improved contact member.
The comtact member 20 comprises a fixed leg portion 21 for securing the contact member to a housing of the jack; a movable leg portion 22 extending substantially in parallel with the fixed leg portion; a substantially U-shaped portion 23 for coupling the fixed and movable leg portions with each other at their one ends; and a projection 21a formed integrally with the fixed leg portion 21 and extending toward the movable leg portion 22, the projection 21a having such a length that a displacement of the movable leg portion 22 toward the fixed leg portion 21 can be limited by an engagement of the projection 22 with the leg portion 22, whereby said fixed leg portion, movable leg portion U-shaped portion and projection are all integrally formed by punching a metal plate. According to such a contact member the projection can effectively limit the displacement of the movable leg portion over the elastic limit and further the contact member can be simply formed by punching.
However after various tests it has been found that in the resilient contact member once the movable leg portion is made in contact with the projection, the movable leg portion could not further move toward the fixed leg portion 21. Therefore if a great force is applied to the movable leg portion by the pin, the jack and/or the pin might be damaged.